Nano-materials have been explored extensively as fundamental building blocks for advanced functional materials. Nanotubes, with large surface area and high aspect ratio, hold the most promise to provide unique and improved properties to new materials. Although there are many different processes of producing nanotubes, organizing and manipulating nanotubes into a particular assembly to create a real world structure at a product scale has been challenging.
A fuel cell has been recognized as one of most promising energy device due to its high energy efficiency and low emission. There are, however, many technical and economical challenges for commercial design and production of fuel cells. Nanomaterials, such as nanotubes, can potentially help overcome some of the challenges. Improvement of fuel cell bipolar plate, for example, is needed in the areas of corrosion resistance, water management capability and durability.
A fuel cell usually consists of a series of membrane electrode assemblies and bipolar plates stacked together in an alternating manner. The membrane electrode assembly is typically made of an ion conductive membrane sandwiched between an anode and a cathode sections each on the opposite side of the membrane. Bipolar plate is a plate like electric conductor having plurality of channels for fluid passage. The reactive gases flow through those channels to reach the anode and cathode sections where electrochemical reactions of the gases take place to generate electricity. The electricity generated from the electrochemical reactions is collected and conducted through the bipolar plate to an external circuit. The bipolar plate, therefore, needs to have high electric conductivity or low contact resistance to avoid energy loss. The bipolar plate also needs to meet very stringent corrosion resistance requirement due to the harsh environment created by the reactive gases, electrochemical reactions and contaminants generated from the membrane electrolyte in the process. In the case of a hydrogen fuel cell, water management is another key challenge. Water is continuously generated in a hydrogen fuel cell and the ion conductive membrane needs to maintain a certain hydration level. When a hydrogen fuel cell is operated at a low current density, for example, at 0.2 A/cm2, there would not be enough gas flow to remove the water generated at the cathode section. Water drops can form in the fluid passages and block the flow of reactive gas. Without the supply of reactant gas, the blocked section of the fuel cell will not produce electricity. Performance of the fuel cell will deteriorate due to non-homogeneous current distribution. Such phenomenon is known as low power stability (LPS). Although there are several recent approaches to improve LPS by making the plate channel surface hydrophilic to spread out condensed water, further improvement in water management is desired.